| Summary: | Abstract Background Ductal carcinoma in situ (DCIS) is an established precursor to invasive ductal carcinoma (IDC) and its coexistence with IDC appear to favor reduced biological aggressiveness. Its prognostic implication and ability to affect clinical outcome has been understudied in Asia. This study aims to explore if concomitant DCIS affects the clinical behavior and outcomes among Asians. Aim Stages I to III breast cancer patients with histological proven IDC, diagnosed and treated in a single institution from June 1, 2004 to June 30, 2014 were included in this study. Statistical analyses were conducted using Χ2 test, independent t test, multivariate logistic regression and Kaplan–Meier test. Methods and Results A total of 818 patients were identified, including 224 and 594 patients with isolated IDC (No‐DCIS) and IDC with coexisting DCIS (IDC‐DCIS) respectively. Patients with IDC‐DCIS were found to have smaller tumors (median: 22 mm, p ≤ .01), estrogen receptor positivity (p = .001), progesterone receptor positivity (p < .001) and associated with better pathological stage (p = .001). Patients with No‐DCIS were 1.6 times more likely to develop disease progression (95% CI: 1.1–2.3, p = .027) and subsequently associated with distant recurrences (20.5% vs. 13.6%, p = .02). The breast cancer specific 5 year overall survival rate for patients with No‐DCIS and those with IDC‐DCIS was 90.9% (95% CI: 86.2%–94.5%) and 93.7% (95% CI: 91.4%–95.5%), respectively (p = .202). Conclusion The presence of DCIS component in IDC among Asians is associated with favorable tumor biological profile, thereby indicating reduced disease aggressiveness. Our study is the first to report the clinical significance in terms of disease progression and distant recurrences among Asians.
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